Refining apparatuses are used in pulp processing for disintegrating and refining fibrous material, e.g. containing lignocelluloses. A typical refining apparatus for working fibrous material is a refiner of a disc-type. In such a refiner apparatus, two discs are rotated in relation to each other separated by a small refining gap. The discs are typically built up of refining segments, one or several, provided with patterns of bars and intermediate grooves that together form refining surfaces. The refining segments are replaced at regular intervals due to considerably wear. They are typically mounted directly on the rotor and stator, respectively, or by means of special segment holders. Refining apparatuses of this type are commonly used for many different types of refining, e.g. for processing of board pulp.
Fibrous material is typically introduced at the centre part of the discs and is refined in the refining gap when successively being transported to a peripheral edge of the discs by means of the forces created by the relative rotation. The discs are typically divided into different portions in radial direction. Closest to the rotational axis, an in-feeding portion is typically provided. Going outwards in the radial direction, the pattern of bars becomes successively denser and comprises typically narrower bars, at the same time as the refining gap is reduced. When changing from a portion with a less dense pattern to a portion with a denser pattern, there are considerations to be made. The flow of fibrous material tends to follow the sides, facing the relative rotational direction, of the coarse bars of the less dense pattern and when the flow meets the denser pattern, only a part of the pattern will initially be exposed for the main amount of the fibrous material. Due to this concentration of flow, the fine refining bars of the denser pattern in front of the ends of the coarse bars of the less dense pattern will experience a high wear. This is troublesome since the structure is relatively thin and has to be replaced relatively often. These effects are particularly noticeable when the change in pattern density is large between the different portions, e.g. what is usually the case in board pulp processing.
An object of the present invention is to provide refining arrangements with improved wear properties, and in particular wear properties in transition regions between portions having different pattern densities.
The above object is achieved by segments and arrangements according to the enclosed patent claims. In general words, in a first aspect, a refining segment, intended for refiners of disc-type for working fibrous material, comprises a first portion having a first pattern of coarse bars and a second portion having a second pattern of fine bars. The second portion is positioned outside the first portion in a radial direction. The second pattern has a higher density of bars than the first pattern. The refining segment further comprises at least one deflector arrangement, protruding from a bar surface of one of the coarse bars. The bar surface is the one facing the intended relative rotational direction. The deflector arrangement has a deflector surface directing a flow of fibrous material away from the bar surface.
In a second aspect, a refining apparatus for working of fibrous material has two opposing refining discs rotatable in relation to each other and separated by a refiner gap. At least one of the two refining discs comprises a first portion having a first pattern of coarse bars and a second portion having a second pattern of fine bars. The second portion is positioned outside the first portion in a radial direction. The second pattern has a higher density of bars than the first pattern. The refining apparatus further comprises at least one deflector arrangement, protruding from a bar surface of one of the coarse bars. The bar surface is the one facing the intended relative rotational direction. The deflector arrangement has a deflector surface directing a flow of fibrous material away from the bar surface.
One advantage with the devices according to the present invention is that the refining discs are provided with a diverger mechanism spreading the flow of fibrous material more evenly over the inlet part to the portion with denser bar pattern, thereby reducing the concentration of wear at limited parts of the fine bars.